Excessive acceleration of an automobile or other vehicle is undesirable because of greater fuel consumption, more rapid tire wear, and increased strain on the vehicle engine. In addition, rapid acceleration tends to be correlated with unsafe driving practices. However, drivers are often unaware of the fact that they are accelerating at a rate that is likely to have any of these unfortunate effects. Thus, the need is presented for an accelerometer suitable for use in an automobile, to provide an indication of acceleration for the driver who, it is assumed, will then endeavor to maintain the acceleration of the vehicle within tolerable limits.
The use of a pendulum to measure acceleration is well known, with the acceleration being given by the product of the acceleration of gravity and the tangent of the angle of inclination of the vertical assumed by the pendulum. It is sometimes found expedient to have an indicating needle magnetically coupled to the pendulum to provide a reading of acceleration. Disclosures of such devices are found in U.S. Pat. Nos. 2,108,695; 2,154,678; 3,044,306; and 3,395,583. In certain other applications, extreme linearity is a desired or necessary characteristic. U.S. Pat. No. 3,498,138 discloses the use of electromagnets and permanent magnets to apply restoring forces so that the sensing pendulum like member is maintained in a neutral position.
One problem shared by many of the prior art devices is a basic lack of sensitivity due to the limited angular excursion possible. For example, a horizontal acceleration equal to the acceleration of gravity will provide an angular excursion of forty-five degrees. For this reason, a need has arisen for a simple accelerometer which is highly sensitive and which can easily be attached to a vehicle at a location sufficient to permit the accelerometer to fairly accurately measure forward acceleration.